A photosite comprises at least one photodiode and at least one isolation trench zone for isolating the photodiode(s).
Image sensors based on semiconductor components benefit from the principle of the conversion of photons into electron/hole pairs in silicon. More precisely, the charges created in the photosensitive zones are stored in the photodiode and then read by an electronic system. This electronic system, which controls the photodiode, comprises, especially when the photodiode is a fully-depleted photodiode, a transfer transistor permitting transfer of the charges stored in the photodiode to a charge collection zone. This charge collection zone forms a sensing node to which a conventional electronic control circuit comprising especially a read transistor is connected.
An imaging device generally comprises photodiodes arranged in a matrix. Each photodiode corresponds to a pixel of an image. The matrix comprises rows of semiconductor photodiodes, each row being bordered by deep isolation trenches. A deep isolation trench comprises a conductive internal portion surrounded by an insulating layer. A photodiode operates in a cycle comprising at least an integration step, a measurement step and a resetting step. The integration step corresponds to the photogeneration of charges and their accumulation during exposure of the photodiode. The measurement step corresponds to the generation of a signal that depends on the number of photogenerated charges accumulated in the photodiode. The resetting step corresponds to the removal of the photogenerated charges.
Under certain conditions, the number of electrons generated during the integration step may exceed the number of electrons that can be stored. If no precautions are taken, the electrons that can no longer be stored in the photodiode may then diffuse into the adjacent photodiodes of the photosite. This results visually in the generation of a white halo or white columns of increasing size on the image. This halo effect between adjacent pixels is called blooming.
Another drawback to which these devices may be afflicted is a lag, during the measurement phase, of the signal generated by each pixel due to the trapping of the electrons while they are being transferred between the deep storage layers and the surface (charge adsorption and re-emission).